Dynamic DNS

[#1]

I am having problems with my router set up:
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Use DynDNS: Yes
Internet Service: Internet
Username: username
Password: ********
IP address: 87.112.167.17
Dynamic DNS service: dyndns
Hostname: systec.dnsalias.net (Update error)
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The information is valid, the router (Thomson ST536v6) reports an update error but does update Dyndns first time but never again.
Has anyone had similar problems?